The linear signal behavior of RF and microwave devices is generally characterized by the well-known S-parameters. In practice, for a majority of the RF and microwave devices and applications the S-parameter approach suffices for characterizing the signal behavior of the device.
However, in recent applications of RF and microwave devices, such as power amplifiers for use in base stations and portable radio equipment of wireless radio communication systems, for achieving optimum RF transmit power at the output antenna of such a device and for providing maximum receiver sensitivity and low interference ratios, there is a need for characterizing the non-linear behavior of such devices. In particular for characterizing the non-linear RF and microwave signal behavior of these devices in a near matched load environment.
RF Integrated Circuits (ICs) are mounted on a Printed Circuit Board (PCB) with varying relative dielectric (epsilon) constants and varying widths of the transmission lines, resulting in variations in the equivalent impedance or load of the RFICs. Knowledge of the effects of these different loads on the non-linear behavior of the devices is valuable to both RFIC manufacturers and circuit designers and other users.
In practice, non-linear behavior of RF and microwave devices is analyzed by loading the device under test using passive or active loadpull techniques. Passive loadpull, however, requires readily expensive tuners. Active loadpull requires the availability of a second excitation source.